In an automobile field, a regulation on a fuel efficiency, CO2 an exhaust gas (mainly nitrogen oxides (NOx), and particulate matters (PM)) becomes tighter every year, and a number of new control schemes for satisfying the regulation are considered as a future control on an internal combustion engine. Among them, a physical quantity detection device used in various types of controls becomes diverse. In particular, physical quantities such as an air, temperature, humidity, and pressure in an intake pipe for the connection to a combustion chamber of the internal combustion engine are necessarily measured with accuracy because the quantities directly influence on the fuel efficiency and an exhaust gas.
The regulation on the fuel efficiency, CO2, and the exhaust gas are calculated and regulated on the basis of a running cycle represented as NEDC of Europe. For a future regulation, not only the regulation values but also a running cycle condition and an on-vehicle diagnosis system (OBD) regulation value are changed.
Presently, the physical quantity detection device to be inserted in the intake pipe generally measures mass flow rate, pressure, and temperature. However, a control using an absolute humidity (an amount of moisture in the air) is received a lot of attention as an internal combustion control in view of the above situation.
Since the moisture in the air affects a flame spread time in a combustion control of the internal combustion engine, a gasoline engine is degraded in combustion efficiency for example. In addition, there is known an influence of an emission increase of PM in a diesel engine as the combustion temperature is lowered.
Herein, the absolute humidity indicates an amount of moisture contained in the air (g gram/kg kilogram), and can be calculated from a temperature, a relative humidity, and a pressure in the air. On the other hand, the relative humidity indicates a ratio (% percent) of the amount of moisture in the air.
As described above, temperature and pressure sensors are used in the automobile field for a long time, but a sensor for measuring the relative humidity in the air flowing in the intake pipe are not much known. Presently, there are disclosures that the humidity sensor is integrally configured to an air flow rate detection device in the automobile field (see PTLs 1 to 3).
The air flow rate detection devices disclosed in PTLs 1 and 2 are integrated with an air flow rate sensor, a humidity sensor, and a pressure sensor. The air flow rate sensor is positioned in a bypass passage through which the air flowing in a main air passage (simply referred to as intake pipe) is taken, and is disposed in a terminal member formed of a metal material. The humidity sensor is positioned in a second bypass passage through which the air flowing in the bypass passage is taken, and mounted in an electronic printed-circuit board. Finally, the pressure sensor is disposed in a housing member. In other words, the respective physical quantity detection sensors are disposed in different members.